Antistatic compositions based on polyamide

ABSTRACT

This antistatic polyamide composition, comprising at least one polyamide and a sufficient amount of carbon black to make it antistatic, is characterized by the fact that the carbon black is at least a carbon black that is selected from among those having a specific BET surface area, measured according to ASTM Standard D 3037-89, from 5 to 200 m2/g, and DBP absorption, measured according to ASTM Standard D 2414-90, from 50 to 300 ml/100 g.

This invention relates to compositions based on polyamide that can beused in particular for the production of single-layer or multilayertubes and/or ducts in the field of transport and/or storage ofhydrocarbons.

In automobiles, under the action of the injection pump, the gasolinecirculates at high speed in the tubes that connect the engine to thetank, whereby these tubes are obtained from compositions that are basedprimarily on polyamide 11 or 12 (RILSAN). In some cases, the rubbing ofgasoline/inside wall of the tube can produce electrostatic charges,whose accumulation can lead to an electric discharge (spark) that canignite the gasoline with catastrophic consequences (explosion). Also, itis necessary to limit the surface resistivity of the inside face of thetube to a value that is generally less than 10⁶ ohms (Ω).

Furthermore, these polyamide-based compositions should meet the othercriteria of the specifications of the gasoline line and in particularcold shock resistance. In addition, the polyamide composition, madeantistatic, should be extrudable: it is therefore sought to limit asmuch as possible its viscosity in the molten state. It should also bechemically resistant to peroxidized gasolines.

It is known to lower the surface resistivity of resins or polymericmaterials by incorporating in them conductive and/or semiconductivematerials, such as carbon black, steel fibers, carbon fibers, particles(fibers, strips, spheres, etc.) that are gold-, silver- or nickel-platedor covered by a fine layer of polymer that is inherently conductive orsemi-conductive.

Among these materials, the carbon black is used more particularlybecause of its great commercial availability and its good performances.

When the level of carbon black is increased in a polymeric composition,the resistivity first changes little. Then, when a critical level ofcarbon black, called percolation threshold, is reached, the resistivitydrops very abruptly until a relatively stable level (plateau zone) isreached, where increasing the carbon black level brings about verylittle change in resistivity.

The technical report “Ketjenblack EC—BLACK 94/01” of the AKZO NOBELCompany indicates that a conductive and/or semi-conductive carbon blackis all the more effective—i.e., it is necessary to add little of it tothe polymer to give it antistatic properties—as its structure isdeveloped. The structure of a carbon black reflects the manner in whichthe basic carbon-containing particles that constitute the carbon blackare arranged in aggregates, even in agglomerates. The structure of acarbon black can be expressed by its specific surface area (measured bythe nitrogen adsorption method—BET method—according to ASTM Standard D3037-89), as well as by its DBP (di-butyl-phthalate) absorption(measured according to ASTM Standard D 2414-90). The carbon blacks thatare marketed by the AKZO NOBEL Company are very structured andcharacterized by a large BET surface area and high DBP absorption. Theyare often designated as extra-conductive carbon blacks. Thanks to theirdeveloped structure, the percolation threshold is reached at a lowaddition rate.

Beyond its electro conductive and/or semi-conductive properties, thecarbon black acts like a filler, such as, for example, talc, chalk,kaolin, and therefore affects many other physical and chemicalproperties.

Thus, one skilled in the art knows that when the proportion of fillerincreases, the viscosity of the polymer/feedstock mixture increases, aswell as the modulus of elasticity of the composition. The increase inviscosity is observed by, for example, a measure of the fluidity index(MWI=melt flow index). Also, when the capacity factor increases, thedurability or resistance to impact of the charged polymer, expressed by,for example, measurement of elongation at break or impact strength,decreases. The increase of the viscosity and the reduction of the impactresistance are all the larger the higher the proportion of filler.

Thus, one skilled in the art naturally prefers to reduce the proportionof filler to impart the desired property to the polymer/feedstockmixture while affecting the other properties, such as viscosity orimpact resistance, as little as possible. Thus, if the task at hand isto obtain a low surface resistivity, one skilled in the art will ratheruse extra-conductive carbon blacks.

It was thus noted that for polyamide 12, with inherent viscosity 1.65(measured at 20° C. for a sample of 0.5 g in 100 g of meta-cresol),plasticized by 11.4% by mass of n-butyl benzene sulfonamide (BBSA) andcontaining at least 6% by mass of Ketjenblack EC 600 jD carbon black ofthe AKZO NOBEL Company (characterized by DBP absorption that is greaterthan 400 ml/g and by a BET surface area that is greater than 1000 m²/g),the surface resistivity on the tube is less than 10⁶ ohms. It was noted,moreover, for this same polyamide, that the plateau zone 10²-10³ ohms)is reached starting at 10% by mass of Ketjenblack EC 600 JD carbonblack.

It seems, however, that this carbon black, that can be designated as“structured” or “more structured,” disperses poorly in the polyamide inthe molten state, which leads to the presence of agglomerates. Theseagglomerates have a negative effect on the impact strength.

It has now been discovered, surprisingly enough, that by going againstthe teaching of the prior art that relates to, on the one hand, theselection of the type of carbon black, and, on the other hand, itsamount used, namely by using a conductive carbon black and/or a “lessstructured” semi-conductive carbon black than the extra-conductivecarbon black above and in addition by using such a carbon black in alarger amount than the preceding extra-conductive carbon black,polyamide compositions that have better impact strength as well asbetter Theological properties (with equivalent resistivity levels) areobtained.

The fact of using a less structured carbon black requires increasing thecontent to obtain the same antistatism level—generally the goal is toproduce a surface resistivity of less than 10⁶ ohms. Despite this higheraddition rate of carbon black, better rheological properties (a lowerviscosity in the molten state, which is demonstrated by a higherfluidity index (MW-I)) and impact strength (impact resistance) areobtained. This is all the more surprising since in general—and asemphasized above—the more the proportion of filler is increased, themore it is precisely these properties that are degraded.

Thus, this invention, residing in the selection of this “lessstructured” carbon black, does not produce a better compromise ofantistatism/other properties, but leads to a polyamide-based antistaticcomposition that has inherently better rheological properties and impactstrength.

This invention therefore first has as its object a composition ofantistatic polyamide, comprising at least one polyamide and a sufficientamount of carbon black to make it antistatic, characterized by the factthat the carbon black is at least a carbon black that is selected fromamong those that have a specific BET surface area, measured according toASTM Standard D 3037-89, from 5 to 200 m²/g, in particular from 20 to100 m²/g, and DBP absorption, measured according to ASTM Standard D2414-90, from 50 to 300 ml/100 g, in particular from 125 to 250 ml/100g. (The measurement of the DBP absorption is that of a pore volume thatis expressed in ml of di-butyl-phthalate per 100 g of carbon black.)

The carbon blacks according to the invention can be designated asconductive or semi-conductive contrary to extra-conductive carbon blacksthat are used according to the prior art, which generally have a BETsurface area that is greater than 500 m²/g and DBP absorption that isgreater than 300 ml/100 g.

Furthermore, the polyamide-based antistatic compositions of theinvention preferably contain 16 to 30% by mass of these “lessstructured” conductive or semi-conductive carbon black(s) and moreparticularly 17.5 to 23% by mass, relative to the total composition.

The polyamide-based antistatic compositions of the prior art, using“more structured” extra-conductive carbon blacks, generally contain 4 to14% by mass, and more particularly 6 to 10% by mass to obtain the sameantistatism level.

Despite the higher level of carbon black, the antistatic compositionsaccording to the invention have a better fluidity and a better impactresistance, as will be illustrated by the examples below.

In terms of this invention, polyamide is defined as the polyamides or PAthat contain aliphatic and/or cycloaliphatic and/or aromatic patterns.

It is possible to cite the polyamides that are obtained bypolycondensation of one or more lactams, of α,ω-amino acids or by anapproximately stoichiometric polycondensation of one or more aliphaticdiamine(s) and one or more aliphatic carboxylic diacid(s). It ispossible to use excess diamine to obtain excess amine terminal groupsrelative to the carboxyl terminal groups in the polyamide.

The lactams contain at least 6 carbon atoms, preferably at least 10. Thepreferred lactams are decalactam, undecalactam, and dodecalactam.

The preferred α,ω-amino acids are the 10-aminodecanoic acid, the11-aminoundecanoic acid, and the 12-aminododecanoic acid.

The aliphatic diamines are α,ω-diamines that contain at least 6 carbonatoms, preferably 6 to 10 carbon atoms, between the terminal aminogroups. The carbon-containing chain can be linear (polymethylenediamine) or branched or cycloaliphatic. Preferred diamines arehexamethylene diamine (HMDA), dodecamethylene diamine, and decamethylenediamine.

The carboxylic diacids can be aliphatic, cycloaliphatic or aromatic. Thealiphatic carboxylic diacids are carboxylic α,ω-diacids that have atleast 4 carbon atoms (not including the carbon atoms of carboxylicgroups), preferably at least 6, in the linear or branchedcarbon-containing chain. The diacids are the azelaic, sebacic and1,12-dodecanoic acids.

By way of illustration of such PA, it is possible to mention:

polyhexamethylene sebacamide (PA-6,10),

polyhexamethylene dodecanediamide (PA-6,12),

poly(undecanoamide) (PA-11),

polylauryllactam (PA-12),

polydodecamethylene dodecanediamide (PA-12,12),

polycapronamide (PA-6),

polyhexamethylene adipamide (PA-6,6).

The PA have a mean molecular mass generally greater than or equal to5000 in number. Their inherent viscosity (measured at 20° C. for asample of 0.5 g in 100 g of meta-cresol) is generally greater than 0.7.

In terms of this invention, PA is also defined as the mixtures ofpolymers that contain at least 50% by weight of the polyamides that aredescribed above where the matrix phase consists of polyamide.

By way of example of mixtures, it is possible to cite the mixtures ofaliphatic polyamides and semi-aromatic and/or ;amorphous polyamides,such as those described in EP 550308, as well as the PA-polyolefinmixtures and in particular those that are described in EP 342066.

According to the invention, PA is also defined as the polyamide-basedthermoplastic elastomers (TPE) that are block copolymers, also calledpolyetheramides or polyether block amides, whose rigid sequences consistof polyamide and crystallizable, flexible polyether sequences.

The compositions according to the invention can also contain at leastone additive that is selected from among:

plasticizers;

impact additives;

phosphoric acid, phosphorus acid or hydrophosphorus acid or theiresters, or sodium salts or potassium salts or combinations of theseproducts;

dyes;

pigments, other than carbon black;

brighteners;

antioxidants;

UV stabilizers;

chain limiters; and

reinforcement fillers.

The plasticizers, whose amount may be up to 30% by mass relative to thetotal composition, can be any plasticizers that are known in the domainof polyamides and are selected in particular from among the benzenesulfonamide derivatives, such as n-butyl benzene sulfonamide (BBSA)(“Ucemid A”), ethyl toluene sulfonamide (“Santicizer 8”) or N-cyclohexyltoluene sulfonamide (“Santicizer 1H”); the hydroxy-benzoic acid esters,such as ethyl-2 hexyl parahydroxybenzolate (EHPB) and decyl-2 hexylparahydroxybenzoate (DHPB); the lactams, such as caprolactam andN-methyl-pyrrolidone; the esters or ethers of tetrahydrofurfurylalcohol, such as oligoethylene oxytetrahydrofurfuryl alcohol; and theesters of citric acid or hydroxy-malonic acid, such as oligoethyleneoxymalonate. A particularly preferred plasticizer is n-butyl benzenesulfonamide (BBSA).

The impact additives, whose amount may be up to 40% by mass relative tothe total composition, are, for example:

1. the polyolefins that can be defined as polymers that comprise olefinpatterns, such as, for example, ethylene, propylene, butene-1 or anyother alpha olefin pattern; by way of examples, it is possible to cite:

the polyethylenes, such as LDPE, HDPE, LLDPE or VLDPE;

polypropylene;

the ethylene/propylene copolymers;

the PE, in particular the VLDPE, obtained with a metallocene as acatalyst;

the copolymers of the ethylene with at least one product that isselected from among the salts or the esters of unsaturated carboxylicacids, or the vinyl esters of unsaturated carboxylic acids.

It is possible to cite in particular LLDPE, VLDPE, polypropylene, theethylene/vinyl acetate copolymers and the ethylene/alkyl (meth)acrylatecopolymers; the density of the polyolefin advantageously can be between0.86 and 0.965, and its MFI can be between 0.3 and 40,

2. the sequenced copolymers, such as the ethylene-propylene rubber (EPR)copolymers, the styrene-b-butadiene-b-styrene (SBS) copolymers, thestyrene-b-isoprene-b-styrene (SIS) copolymers, theethylene-b-propylene-b-diene (EPDM) copolymers, theethylene-b-propylene-b-butadiene or isoprene copolymers, thestyrene-b-ethylene-butene-b-styrene (SEBS) copolymers, such as thecopolymer that is marketed under the name “KRATON” by the Shell Company,

3. the enhanced-function polyolefins that can be defined as polymersthat comprise alpha-olefin patterns and epoxide or carboxylic acid orcarboxylic acid anhydride patterns.

By way of examples, it is possible to cite polyolefins 1) and sequencedpolymers 2) that are grafted by unsaturated epoxides, such as theglycidyl (meth)acrylate and/or by carboxylic acids, such as(meth)acrylic acid and/or by unsaturated carboxylic acid anhydrides,such as the maleic anhydride.

It is also possible to cite:

the copolymers of ethylene, of an unsaturated epoxide and optionally anester or a salt of unsaturated carboxylic acid or a vinyl ester ofsaturated carboxylic acid. These are, for example, the ethylene/vinylacetate/glycidyl (meth)acrylate copolymers or the ethylene/alkyl(meth)acrylate/glycidyl (meth)acrylate copolymers; by way of examples ofthe latter, it is possible to mention those that are marketed under thename “LOTADER” by the ELF ATOCHEM Company;

the copolymers of ethylene, an unsaturated carboxylic acid anhydrideand/or an unsaturated carboxylic acid that can be partially neutralizedby a metal (Zn) or an alkali (Li) and optionally an unsaturatedcarboxylic acid ester or a saturated carboxylic acid vinyl ester. Theseare, for example, the ethylene/vinyl acetate/maleic anhydride copolymersor the ethylene/alkyl or aryl (meth)acrylate/maleic anhydride copolymersor else the ethylene/Zn or Li (meth)acrylate/maleic anhydridecopolymers;

the polyethylene, polypropylene, the propylene ethylene copolymers thatare grafted or copolymerized with an unsaturated carboxylic acidanhydride then condensed with a monoamino polyamide (or a polyamideoligomer). These products are described in European Patent EP 342066.

Advantageously, the enhanced-function polyolefin is selected from amongthe ethylene/vinyl acetate/maleic anhydride copolymers, theethylene/propylene copolymers with propylene predominating, grafted bymaleic anhydride then condensed with monoamino polyamide 6 or monoaminooligomers of caprolactam.

Very particularly, the ethylene—alkyl or aryl (meth)acrylate—unsaturateddicarboxylic acid anhydride co- or terpolymers that comprise 77 mol % to99.2 mol % of at least one ethylene-derived pattern, 0 to 20 mol % of atleast one alkyl or aryl (meth)acrylate-derived pattern and 0.8 to 3 mol% of at least one unsaturated dicarboxylic acid anhydride-derivedpattern and that have a fluidity index of between 0.1 and 400 g/10minutes measured according to NFT Standard 51-016 (190° C./feedstock of2.16 kg) can also be cited; whereby the alkyl groups of the alkylacrylate or methylacrylate that fall within these terpolymers can belinear, branched or cyclic and comprise up to 10 carbon atoms; asexamples of alkyl (meth)acrylate that fall within the composition ofthese terpolymers, it is possible to cite methyl acrylate, ethylacrylate, n-butyl acrylate, isobutyl acrylate, hexyl ethyl-2 acrylate,cyclohexyl acrylate, ethyl methacrylate, and very particularly ethylacrylate, n-butyl acrylate and methyl acrylate; as examples ofunsaturated dicarboxylic acid anhydrides that fall within the definitionof these co- or terpolymers, it is possible to cite the itaconicanhydride, the citraconic anhydride, the methyl-2 maleic anhydride, thedimethyl-2,3 maleic anhydride, the bicyclo[2.2.2]-oct-5-ene2,3-dicarboxylic anhydride, preferably the maleic anhydride; aspreferred examples of these unsaturated dicarboxylic acidalkyl-anhydride ethylene-(meth)acrylate terpolymers, it is possible tocite those that are marketed under the name “LOTADER” by the ELF ATOCHEMCompany,

4. the ionomers, ethylene/(meth)acrylic acid copolymers, such as the onethat is marketed under the name “SURLYN” by the DuPONT Company.

As examples of pigments, it is possible to cite titanium dioxide, cobaltoxide, iron oxide, nickel titanate, organic pigments such as thederivatives of phthalocyanine and anthraquinone.

As examples of brighteners, it is possible to cite the thiophenederivatives.

The antioxidants are, for example, copper iodide combined with potassiumiodide, the occupied phenol derivatives and occupied amine derivatives.

As UV stabilizers, it is possible to mention the resorcin derivatives,the benzotriazoles or the salicylates.

As chain limiters, it is possible to use monocarboxylic acids ordicarboxylic acids or aliphatic monoamines or aliphatic diamines.

Examples of reinforcement fillers are wollastonitite, glass balls,kaolin, talc, mica, the mixture of quartz, mica and chlorite that isknown under the name of “plastorite,” calcium carbonate and/or magnesiumcarbonate, glass fibers, boron nitride fibers and carbon fibers.

The compositions according to the invention can be obtained in a knownway by any technique of mixing components in the molten state such as,for example, the extrusion or compounding on a single- or double-screwextruder, on a co-mixing machine or by any other continuous orintermittent technique, such as, for example, with an internal mixer.

In particular, on a co-mixing machine-type extruder, it is possible tointroduce the carbon black(s) in a molten zone, the granules of thepolyamide(s), if necessary modified by at least one additive as definedabove, whereby a portion is introduced into the feed hopper and aportion is introduced with the carbon black(s).

This invention also relates to the processes for transformation of saidcompositions, as well as the articles that are obtained. The articlesthat are obtained can be tubes, films, pipes, plates, fibers, etc. Thesematerials or articles can be single-layer or multilayer. In the case ofmultilayer materials or articles, the layer that is most exposed to theaccumulation of the electrostatic charges will be based on a compositionaccording to the invention. The invention makes it possible inparticular to use an antistatic and shock-resistant single- ormultilayer tube for the transport and/or storage of hydrocarbons and inparticular gasoline. Among all of the conventional transformationmethods used in the thermoplastics industry that are suitable for theproduction of articles, very particularly the extrusion and coextrusiontechniques will be cited.

The following examples illustrate this invention without, however,limiting its scope.

EXAMPLES 1 to 3

As follows, respectively non-antistatic polyamide compositions(reference composition), antistatic polyamide compositions (comparisoncomposition) and antistatic polyamide compositions (composition of theinvention) that have the formulations that are given in Table 1 areprepared.

TABLE 1 1 2 3 anti- non- static anti- anti- (for static Example staticcom- (of the Formulation of the polyamide (refer- par- inven-composition . . . ence) ison) tion) PA 12 that has an inherent 84 76 62viscosity of 1.65 n-butyl benzene sulfonamide  4  4  4 Thermoplasticelastomer with a 12 12 12 polyether block amide-type polyamide base witha Shore D hardness equal to 42 and a melting point of 147° C.Extra-conductive carbon black —  8 — marketed by the AKZO NOBEL Companyunder the name “Ketjenblack EC 600 JD,” characterized by a DPBabsorption that is greater than 400 ml/g and by a BET surface area thatis greater than 1000 m²/g Carbon black marketed by the M.M.M. — — 22Company under the name “Ensaco 250 Granular,” characterized by DBPabsorption of about 190 ml/g and by a BET surface area of about 65 m²/g

To prepare the composition of Example 1, granules of plasticizedpolyamide that is modified by the polyether block amide are introducedinto the feed hopper of a co-mixing-machine-type extruder. The extrusionmaterial temperatures are typically on the order of 240 to 270° C. Theflow rate is 15 to 20 kg/h.

To prepare the compositions of Examples 2 and 3, the carbon black isintroduced into a molten zone with a force-feed hopper on a BUSSco-mixing-machine-type extruder, whereby a portion of the granules ofplasticized polyamide that is modified by polyether block amide isintroduced into the feed hopper, and a portion is introduced with thecarbon black. The temperatures of the extrusion material are typicallyon the order of 240 to 270° C. The flow rate is 15 to 20 kg/h.

EXAMPLE 4 Measure of the Fluidity Index ISO Standard 1133.91)

The fluidity index (MFI) of each of the compositions of Examples 1 to 3is measured (in g/10 minutes) at 235° C. under 10 kg (ISO Standard1133:91). The tested samples contain less than 0.1% of moisture.

Measure of Surface Resistivity Test indicated in paragraph 7.9“Electrical Resistance” of SAE XJ Standard 2260)

The compositions of Examples 1 to 3 are extruded in the form ofsingle-layer tubes with an inside diameter of 6 mm and an outsidediameter of 8 mm, on a single-screw extruder that is equipped with ascrew with a diameter of 45 mm, adapted to the extrusion of polyamidesat temperatures of 210 to 250° C.

Cylindrical copper electrodes are introduced at the ends of a tube thatis 100 mm in length. A suitable voltage is applied to these electrodes,and the current is measured. The resistance that is thus measured(coarse measurement) is then multiplied by the inside circumference ofthe tube, then divided by the distance between electrodes; the surfaceresistivity that is expressed in ohm (Ω) is obtained.

Multiaxis Impact Test (ISO Standard 6603-2:89)

The compositions of Examples 1 to 3 are injected onto a press in theform of plates at temperatures of 250 to 270° C. These plates have thefollowing dimensions: 100×100×2 mm and make it possible to carry outmultiaxis impact tests at a rate of 4.3 m/s. In this test, the totalenergy that is absorbed (in joules) by the composition during the impactis measured. The type of breaking pattern is also noted: brittle orductile fracture. These tests are carried out at −30° C. The plates areconditioned for 15 days at 50% relative moisture before being tested.

Test of Impact on the Tube Test indicated in paragraph 7-6 “ColdTemperature Impact” of SAE XJ Standard 2260

The compositions of Examples 1 to 3 are extruded in the form of tubes asindicated for the measure of surface resistivity.

A mass of 0.912 kg strikes a tube perpendicularly from a height of 305mm. A tube passes the test if after impact it preserves a resistance tothe explosion (explosion pressure) that is greater than 70% of theexplosion pressure of a non-impacted tube. If this is not the case, thetube is considered broken. The tubes are tested at −40° C. The tubes areconditioned for 15 days at 50% relative moisture before being tested.

The results are recorded in Table 2,

TABLE 2 Impact on the Multiaxis Tube Polyamide Impact Number CompositionFluidity Surface Total of items of the Index (g/10 Resistivity Absorbedbroken/ Example min.) (Ω) Energy (J) 10 1 >12 >10¹³ ≧60, OC/10(reference) ductile 2 (for 2-4 10²-10⁴ ≦10, ≧5C/10 comparison) brittle 3(of the 6-8 10²-10⁴ ≧50, ≦IC/10 invention) ductile

What is claimed is:
 1. An antistatic polyamide composition comprising atleast one polyamide and 16-30% by mass of carbon black based on thetotal composition to make it antistatic, characterized by the fact thatthe carbon black is at least a carbon black that is selected from amongthose that have a BET specific surface area, measured according to ASTMStandard D 3037-89, from 20 to 100 m²/g, and DBP absorption, measuredaccording to ASTM Standard D 2414-90, from 125 to 250 ml/100 g. 2.Articles obtained by extrusion, in particular single-layer tubes, orelse multilayer tubes that are formed by coextrusion, whereby the layerthat is most exposed to the accumulation of electrostatic charges isbased on the polyamide composition as defined in claim
 1. 3. A method ofproviding to a polyamide composition a plateaued volumetric resistivity,an increased impact strength and an improved fluidity, said methodcomprising adding to a polyamide composition 16-30% by mass of carbonblack based on the total composition, said carbon black having a BETspecific surface area, measured according to ASTM Standard D 3037-89,from 20 to 100 m²/g, and DBP absorption, measured according to ASTMStandard D 2414-90, from 125 to 250 ml/100 g.
 4. A method according toclaim 3, wherein the carbon black is present in a concentration of 17.5to 23% by mass relative to the total composition.
 5. A polyamidecomposition according to claim 1, wherein the carbon black(s) arepresent at a concentration of 17.5 to 23% by mass relative to the totalcomposition.
 6. A polyamide composition according to claim 1, wherein italso contains at least one additive that is selected from the groupconsisting of: plasticizers; impact additives; phosphoric acid,phosphorus acid or hydrophosphorus acid or their esters, or sodium saltsor potassium salts or combinations of these products; dyes; pigments,other than carbon black; brighteners; antioxidants; UV stabilizers;chain limiters; and reinforcement fillers.
 7. A polyamide compositionaccording to claim 6, wherein the plasticizers are selected from amongbenzene sulfonamide derivatives, hydro-benzoic acid esters, lactones,esters or ethers of tetrahydrofurfuryl alcohol and esters of citric acidor hydroxymalonic acid.
 8. Polyamide composition according to claim 7,wherein the plasticizer is n-butyl-benzene sulfonamide (BBSA). 9.Polyamide composition according to claim 6, wherein the amount ofplasticizer(s) goes up to 30% by mass relative to the total composition.10. A process comprising extruding the polyamide composition as definedin claim 1 so as to form extruded articles.
 11. A process according toclaim 10, wherein on a co-mixing-machine-type extruder, the carbonblack(s) are introduced in a molten zone, a portion of the granules ofthe polyamide(s), optionally modified by at least one additive selectedfrom the group consisting of plasticizers; impact additives; phosphoricacid, phosphorus acid or hydrophosphorus acid or their esters, or sodiumsalts or potassium salts or combinations of these products; dyes;pigments, other than carbon black; brighteners; antioxidants; UVstabilizers; chain limiters; and reinforcement fillers, being introducedin the feed hopper, and a portion being introduced with the carbonblack(s).
 12. Articles obtained from a polyamide composition as definedin claim 1.